Pumping system and method

ABSTRACT

A pumping method and system for cryogenic storage reservoirs such as on cargo ships. A single liquid transmitting casing extends to the lower portion of the reservoir. A normally closed spring biased foot valve is mounted on the lower end of the casing. A pump and motor unit slidably mounted in the casing opens the foot valve when resting thereon. Operation of the pump and motor unit allows liquid to be pumped out of the reservoir through the casing to a port at the upper end of the casing. When it is desired to fill the reservoir the pump and motor unit is either lifted off the foot valve, or withdrawn from the casing, so that the foot valve closes. Thereafter liquid is introduced through the port at the upper end of the casing. When sufficient pressure occurs to open the spring biased foot valve, either due to pressure applied at the upper end of the casing or due to the liquid level differential between the casing and the reservoir, the reservoir may be filled. Thus, only a single casing is required for filling and discharging the reservoir. A special valve guide for the foot valve poppet is provided to prevent fluttering of the same during the filling operation.

United States Patent [1 1 [111 3,876,120

Haesloop et al. Apr. 8, 1975 l l PUMPlNG SYSTEM AND METHOD [57] ABSTRACT [75] Inventors: William G. Haesloop, Dana Point; A pumping method and system for cryogenic storage J rg GerflkiOS, 511m?) A1111. bOih reservoirs such as on Cargo ships. A single liquid transof Calif. mitting casing extends to the lower portion of the res- [73] Assigneei lmemaflnnal Telephone and ervolr. A normally closed spring biased foot valve [5 mounted on the lower end of the casing. A pump and Telegraph Corporanon New York motor unit slidably mounted in the casing opens the NY foot valve when resting thereon. Operation of the [22] Filed: Jan. 14, 1974 pump and motor unit allows liquid to be pumped out 2| A N J 4 1 of the reservoir through the casing to a port at the I pp] 0 33 353 upper end of the casing. When it IS desired to fill the reservoir the pump and motor unit is either lifted off l 222/333 the foot valve. or withdrawn from the casing, so that [51] Int. Cl. F04b 17/00 the foot valve closes. Thereafter liquid is introduced Field Of Search through the port at the upper end of the casing. When l /350. 2. H3; 220/44 3. 35 sufficient pressure occurs to open the spring biased foot valve. either due to pressure applied at the upper [56] R f r nC S C t d end of the casing or due to the liquid level differential UNlTED STATES PATENTS between the casing and the reservoir. the reservoir may be filled. Thus. only a single casing is required for filling and discharging the reservoir. A special valve guide for the foot valve poppet is provided to prevent fluttering of the same during the filling operation.

2.588.869 3/1952 Pinuire l4l/ll3 3.734.149 5/1973 Hansel l4l/35O Primary Eraminer-Stanley H. Tollberg Atlurney. Agent. or FrrmThomas L. Peterson 13 Claims 6 Drawing Figures FIGS.

FIG.4.

PUMPING SYSTEM AND METHOD BACKGROUND OF THE INVENTION The present invention relates generally to a method and system for pumping cryogenic fluids, and, more particularly, to a submersible pumping system for filling and discharging a cryogenic fluid reservoir such as the hold of a cargo ship.

The present invention constitutes an improvement upon the submersible pumping system disclosed in U.S. Pat. No. 3,369,715 to James C. Carter. In such system a pump and motor unit is lowered into a vertical ex tending through a storage reservoir for liquified gases. The unit trips a foot valve at the bottom of the casing to communicate the pump inlet with the liquid in the reservoir. The centrifugal pump of the unit pumps the liquid into the casing where it flows upwardly to an outlet port at the top of the casing. When the unit is raised off the foot valve, the casing is sealed from the reservoir so that the unit may be removed for repair or replacement without loss of the liquified gases or without the hazards of venting flammable gases to the local atmosphere.

To date, submersible pumping systems of the type disclosed in the aforementioned Carter patent are utilized only for pumping liquid from the storage reservoir. In order to fill the reservoir, such as the hold of a cargo ship, a second casing usually is provided which extends to near the bottom of the reservoir. This casing has an open lower end so that liquid may be pumped downwardly through the casing to fill the reservoir. Occasionally, fluid is introduced into the vapor ullage space above the stored liquid. This manner of tank filling is performed seldomly however. Thus, in presently known pumping systems of the type to which the present invention pertains, usually two separate casings are provided in the reservoir, one for filling the reservoir and one for discharging liquid from the reservoir.

It is the object of the present invention to provide a reservoir pumping system which requires less material to manufacture and is less costly to operate than the system most often used discussed above.

SUMMARY OF THE INVENTION According to the principal aspect of the present invention, the casing utilized for discharging liquid from the cryogenic storage reservoir or the like discussed above is also utilized for filling the reservoir, and the separate filling casing is eliminated. More specifically, the pump and motor unit mounted in the casing is either fully withdrawn from the casing or lifted sufficiently to allow the foot valve at the lower end of the casing to close. Thereafter, liquid is introduced through the port at the upper end of the casing under sufficient pressure or liquid head to open the foot valve thus filling the storage reservoir. Upon cutting off the flow of liquid into the casing, the spring biased foot valve automatically closes. Thus, the foot valve normally utilized for discharging liquid from the storage reservoir functions as a check valve allowing liquid to flow into the reservoir when liquid is introduced under pressure into the upper end of the casing. Therefore, the present invention inexpensively eliminates the separate filling casing employed in pumping systems presently in use.

According to another aspect of the invention, the foot valve is mechanically opened thereafter liquid is introduced through the port at the upper end of the casing to fill the storage reservoir.

According to a further aspectof the invention, there is provided a foot valve poppet guide which includes a flat support plate that engages the back of the poppet when the valve is fully open. This arrangement prevents fluttering of the foot valve during the filling operation which could cause damage to the valve and the casing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a fragmentary, broken, somewhat diagrammatic vertical sectional view of a storage reservoir equipped with the vertical casing having a foot valve at its lower end constructed in accordance with the present invention, the valve being shown in its open position;

FIG. 2 is an enlarged partial sectional view ofthe foot valve illustrated in FIG. 1 but shown in its normally closed position;

FIG. 3 is a horizontal sectional view taken along lines 3-3 of FIG. 2;

FIG. 4 is an enlarged sectional view similar to FIG. 2 showing the foot valve in its open position;

FIG. 5 is a diagrammatic view similar to FIG. 1 of a vertical casing embodying a bypass chamber in accordance with an alternative form of the present invention with the foot valve shown in its closed position; and

FIG. 6 is a perspective view ofa weight for mechanically opening the foot valve according to another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reference numeral 10 in FIG. I designates a storage tank, such as the hold of a ship or the like, provid ing a reservoir R for liquified gas or cryogenic material such as natural gas, methane, butane, propane. ammonia, ethylene, or the like. The liquid level of the liquified material in the reservoir R is shown close to the roof I2, as illustrated at L, and the space S between the top of the liquid and the roof I2 is filled with gas boiling off from the liquid and pressurizing the reservoir to the vapor pressure of the liquid at the applicable tempera ture.

A cylindrical casing or tube 14 extends vertically through the tank I0 from the top to the bottom thereof and extends above the roof 12 as shown. The bottom of the casing carries a foot valve I6 normally biased to a closed position by springs 18 and effective to seal off the interior 20 of the casing from the reservoir R.

The top of the casing 14 is closed by a cover 22 carrying a sealing gland 24 which is raised and lowered by a hand wheel 26 or some other means. The cover also carries a junction box 28 for an electrical connection.

A pump and motor unit 30 is suspended in the casing I4 from the sealing gland 24 by tension member 31 which may be tubing, pipe or cable. Spring loaded guides 34 with roller 36 on their ends may be mounted at intervals on the tension member 31 to guide it centrally in the casing I4.

The junction box 28 is connected through a cable 38 to a stack junction box 40 on the top of the unit 30 for supplying electrical current to the motor of the unit.

When the unit 30 is lowered to the bottom of the casing I4, it rests on the foot valve 16. The weight of the unit is sufficient to open the foot valve, as seen in FIG. 1, and liquid from the reservoir R will flow to the inlet ofthe pump to be propelled through the unit out ofthe annular opening therearound, filling the casing 14 and discharging through an outlet port 42 at the top end of the casing. A valve 44 is provided in the outlet port 42. When the hand wheel 26 is manipulated through the sealing gland 24, the unit is lifted off the foot valve 16, whereupon the springs 18 close the valve sealing off the interior of the casing 14 from the reservoir R. Liquid gaseous fluid in the sealed off casing can be purged therefrom back to the reservoir R by introducing a purging gas. such as nitrogen. through an inlet connection 46. A pipeline 48 connects the casing with the top ofthe reservoir R. Shutoff valve 50in this pipeline prevents backflow during the pumping operation. Further, a check-and-vent valve 52 in the pipeline 49 vents the casing 14 when valve 50 is open following a pump shut down which could cause considerable liquid evaporation for certain style pumps. The structure and opera tion of the assembly shown in FIG. 1 is more fully de scribed in the aforesaid Carter U.S. Pat. No. 3,369,715. Reference is also made to US. Pat. No. 3,652,186 to James C. Carter which describes a preferred pump and motor unit for use in the system.

As stated previously herein, the aforementioned Car ter system is employed only for discharging liquid from the interior of a reservoir. Liquid is introduced into the reservoir by a separate filling conduit or casing. ln accordance with the present invention, the filling casing in the conventional pumping system is eliminated and the filling operation is performed through the discharge casing 14. Preferably, this is accomplished by purging the casing 14 with an inert purging gas and withdrawing the pump and motor unit 30 from the upper end of the casing by removing the cover 22. The cover is then replaced on the upper end of the casing and liquid is introduced into the casing through the port 42 by means of a pump 54 or by gravity flow. The liquid may be in troduced under pressure sufficient to overcome the force of the springs IS in the foot valve, thus forcing the valve open. or the differential liquid levels between the casing interior and the reservoir may be maintained at a level sufficient to hold open the foot valve thereby allowing liquid to fili the reservoir R. When the valve 44 is closed, the foot valve 16 closes under the force of the springs 18. Thus, the foot valve functions as a check valve. The liquid is conveyed to the reservoir through the casing 14 for a sufficient time to fill the reservoir to a predetermined level, which may be the level L or below that level as desired.

lt generally requires about four hours or more to remove the pump and motor unit 30 from the casing 14. It is not always practical to remove the pump and motor unit at each loading terminal ofa ship. Therefore it is sometimes necessary to leave the unit in the casing 14 during the filling operation. The filling operation could be performed through the casing 14 with the pump and motor unit 30 seated on the foot valve 16 to open the same. However, this mode of operation would have the disadvantage that all the liquid introduced through the casing would flow through the pump housing 56. This is because the pump housing is formed with a downwardly facing frustoconical surface 59 at the lower end of the casing 14 which prevents flow of liquid around the unit 30 to the bottom of the casing. Flow of liquid through the pump housing 56in the direction opposite to its normal direction of flow will run the impeller in the pump backward, causing unnecessary wear and possibly overspeed of the pump due to the high flowrate of liquid used at shipping terminals. Also, flowback through the pump of the unit 30 creates a significant pressure drop thereby slowing the filling operation. If it is necessary that the unit remain in the casing 14 during the filling operation, it is preferable that the unit be lifted sufficiently to cause the foot valve 16 to close under the force of the springs 18. The liquid introduced through the port 42 in the casing 14 will flow downwardly around the pump and motor unit 30 and will act upon the foot valve directly to open the same. The majority of the flow takes place around the unit 30 since the annular channel defined between the unit and the casing 14 presents less restriction to flow than does the flow passages through the pump housing 56.

Reference is made to FIG. 5 of the drawings which shows a modified form of the casing l4 which may be utilized with the previously described filling method in which the pump and motor unit 30 remains within the casing during the filling operation. ln this embodiment, the casing 14 is formed with an enlarged section 61 adjacent to its lower end. A plurality of radially inwardly extending guide supports 62 are formed on the casing section 61, at least three of such supports being required. A cylindrical guide 64 having the same diameter as casing 14 is mounted on the inner periphery of the guide supports 62. This arrangement assures that the unit 30 will be coaxially guided for movement within the casing 14, yet a bypass chamber of substantial flow area will be provided between the unit and the casing section 61. Preferably this bypass chamber has an area substantially equal to the cross-sectional area of the casing 14 above the section 61. Also, as will be appreciated, the enlarged section 61 forming the bypass chamber is positioned so that when the pump and motor unit 30 is mounted therein, the unit will be lifted off the foot valve 16 allowing the valve to close. By this arrangement, liquid introduced through the port42 will flow in an almost unrestricted fashion past the pump and motor unit 30 to blow open the foot valve [6 allow ing the filling of the reservoir R.

Reference is now made to FIGS. 2-4 which illustrate the details of structure of the foot valve 16 of the present invention. The valve is mounted in a generally cylindrical housing formed within an upper outwardly extending flange 72 and a lower outwardly extending flange 74. The flange 72 is fixed to an outwardly ex tending flange 76 on the lower end of the casing 14 by suitable connecting means, not shown. An annular recess 78 is formed on the bottom surface 80 of flange 74 adjacent to the inner periphery of the flange. An annular sealing element 82, formed of a suitable material, such as an elastomer, plastic, soft metal or the like, is mounted in the recess 78. The sealing element is retained in the recess by a retaining ring 84 fixed to the flange 74 by screws 86. As will be noted, a downwardly extending lip 88 is formed on the flange 74 inside the sealing element 82 to protect the element 82 from damage due to liquid passing downwardly through the valve.

The foot valve 16 comprises a relatively flat circular plate 90 formed with a central, upwardly extending hub 92. The plate 90 has upstanding ribs 94 at spaced intervals therearound carrying a shroud fitting 96 which abuts the bottom of the pump and motor unit 30 when the latter is seated on the foot valve. The plates 90, ribs 94 and fitting 96 form the valve poppet of the foot valve. A plurality of vertically extending bolt 98 are mounted in the outer region of the foot valve plate 90 at circumferentially spaced intervals around the plate. only one of such bolts being illustrated in FIG. 2. A re tainer 100 is fixedly mounted by a pin 102 to the upper end of each bolt 98. A hearing grommet 104 is mounted in the flange 74 for each ofthe bolts 98. Each spring 18 is in the form of a coil spring which extends between the grommet 104 and retainer 100. The springs 18 bias the foot valve poppet in the upward direction. An annular valve rim 106 is formed on the upper surface of the plate 90 coaxial with the axis of the housing 70 and concentric with the sealing element 82. The springs 18 bias the valve rim 106 into sealing engagement with the sealing element. The structure of the foot valve disclosed so far is generally the same as that disclosed in the aforementioned Carter patents. Such arrangement is entirely satisfactory when the easing 14 is utilized simply for discharging liquid from the reservoir R. However, during the filling operation liquid is introduced into the casing 14 at about 3,500 gallons per minute. At this extremely high flow rate, the foot valve would be unstable, causing fluttering of the valve. Such fluttering could cause high pressure purges through the system, resulting in damage to the sealing element 82 and the casing 14.

According to another feature of the invention. means is provided for the foot valve 16 to assure that the poppet will not flutter during the filling operation. To this end. there is provided a flat bottom structure 110. The bottom structure 110 may be simply in the form of a circular plate coaxial with the axis of the housing 70 and casing 14. Preferably. however, in order to save material the bottom structure is in the form ofa wheel comprising a central hub 112 with a circular rim 114 concentric with and spaced from the hub. A plurality ofspoke elements 115 connect the rim to the hub three of such elements being shown in FIG. 3. Obviously a larger number of spoke elements could be utilized if desired. A plurality of upwardly extending support webs 116 are integrally formed on the rim 114. The upper ends of these webs extend through radially extending slots 118 in the outer periphery of the foot valve plate 90 and abut the lower surface of the flange 74. The bottom structure 110 is fixed to the flange 94 by means of screws 120 which thread into the upper ends ofthe support webs 116. By this arrangement. the bottom structure 110 is firmly attached to the lower end of the casing 14 yet the foot valve poppet is free to move vertically. When the poppet is in its fully open position as seen in FIG. 4. the poppet seats firmly against the flat bottom structure which reduces fluttering of the poppet.

Guide means, generally designated 122, is provided between the flat bottom structure 110 and the foot valve to assure that no fluttering of the poppet occurs. Such guide means includes a vertically extending cylindrical bearing guide 124 mounted centrally within the hub 112 of the structure 110. This guide is preferably formed of bronze. The guide slidably receives a rod 126 having a head 128 which is fixed to the hub 92 of the valve plate 90 by means of screws 130, only one being shown. As will be appreciated. the rod 126 could be mounted on the bottom structure 110 and the cylindrical guide 124 on the foot valve 16.1n any event. the co operating rod and cylindrical guide assure that the foot valve moves vertically without fluttering.

As will be appreciated, when the pump and motor unit 30 is mounted in the casing so as to rest on top of the foot valve 16. the valve will open allowing the liquid to be discharged from the reservoir upwardly through the casing 14. When it is desired to fill the reservoir. the pump and motor unit may be either lifted off the foot valve to close the same or entirely withdrawn from the casing. so that liquid may be introduced downward through the casing to force the foot valve open to fill the reservoir. When the foot valve is urged downwardly to an open position by the force of the fluid pressure exerted on the upward surface thereof. or by liquid head, the foot valve will assume the position illustrated in FIG. 4 wherein fluid is free to flow from the casing outwardly through the spaces between the supporting webs 116 into the reservoir. Thus. only a single fluid transmitting casing is required for filling and discharging the reservoir. Moreover. the bottom structure and guide members 124 and 126 may be readily assembled to existing pumping systems as disclosed in the aforementioned Carter patents. allowing the discharge casing therein to be utilized for filling also.

According to another embodiment of the invention. the foot valve 16 is mechanically opened and thereafter liquid is introduced through port 42 to fill the reservoir through the casing 14. This mode of operation is required for some installations where the pump and motor unit is not mounted in the casing 14 and special inert gas purging procedures are utilized. not permitting the foot valve to be opened by fluid pressure. The means for mechanically opening the foot valve may comprise a plurality of vertical rods not shown) posi tioned around the casing 14. with their lower ends at tached to the foot valve poppet and their upper ends extending above the reservoir roof 12 where they may be manipulated. Alternatively. a weight simulating the pump and motor unit 30 may be used for opening the foot valve. Such a weight is shown in FIG. 6 and is gen erally indicated by reference numeral 130. The weight comprises a central cylindrical member 132 having an eyelet 134 at its upper end for connection to a suitable suspension line. not shown. Spring loaded guides 136 with rollers 138 on their ends are provided at the upper end of member 132 to guide the weight in the casing 14. A ring 140 is supported by webs 142 to the lower end of member 132. Guide wheels 144 are provided on the ring to further assist guiding of the weight in the discharge casing. A frustoconical surface 146 is formed on the bottom edge of ring 140 which is complementary to the frustoconical surface 59 at the bottom of the easing. The lower end of member 132 is formed with a coaxial circular projection 148 which extends below ring 140 and has a diameter less than the inner diameter of the shroud fitting 96 of the foot valve poppet. Thus. when the weight is lowered into the discharge casing the projection 148 thereon will engage the head 128 of the foot valve guide. The structure has sufficient weight to force the poppet to its open position. After the foot valve has been opened. the reservoir may be filled by introducing liquid into the casing 14 through the port 42. It will be appreciated that due to the hollow configuration of weight 130, the weight will create only a minimum resistance to liquid flow through the casing.

What is claimed is:

l. A method of filling a reservoir with a liquid and withdrawing the liquid from the reservoir comprising the steps of:

providing a casing in said reservoir extending from the top to a bottom portion of the reservoir, a port at the upper end of said casing. a spring biased normally closed valve means depending from the bottom of said casing. a pump and motor unit slidably received in said casing and resting on said valve means, the weight of said pump and motor unit on said valve means opening the same to communicate the bottom of said casing to said reservoir;

lifting said pump and motor unit off of said valve means to close said valve means;

conveying said liquid into said casing through said port under sufficient pressure or sufficient liquid head to open said valve means and for sufficient time to fill said reservoir to a predetermined level;

thereafter lowering said pump and motor unit onto said valve means to open the same; and

energizing said pump and motor unit to withdraw liquid from said reservoir through said casing.

2. A method as set forth in claim 1 including the step withdrawing said pump and motor unit from said casing prior to conveying said liquid into said casing.

3. A method as set forth in claim 1 including the steps of:

providing a bypass chamber in said casing; and

lifting said pump and motor unit into said chamber prior to conveying said liquid into said casing,

4. A method of filling a reservoir with a liquid and withdrawing the liquid from the reservoir comprising the steps of:

providing a casing in said reservoir extending from the top to a bottom portion of the reservoir, :1 port in the wall of said casing near the upper end thereof. a spring biased normally closed valve means depending from the bottom of said casing adapted to be opened to communicate the bottom of said casing to said reservoir by applying a force to the upper surface of said valve means and a removable cover closing the upper end of said casing;

conveying said liquid into said casing through said port under pressure or at sufficient differential liquid head to apply a force to said upper surface sufficient to open said valve means and for sufficient time to fill said reservoir to a predetermined level;

removing said cover from said casing;

sliding a pump and motor unit into said casing through said upper end thereof. lowering said unit onto said valve means to open the same; and

energizing said pump and motor unit to withdraw liquid from said reservoir through said casing.

5. A pumping system for a liquid storage reservoir of a ship or the like comprising:

a single casing in said reservoir extending from a top to a bottom portion of said reservoir;

a port in said casing near the upper end thereof;

a spring biased normally closed valve means depending from the bottom of said casing adapted to be opened to communicate the bottom of said casing to said reservoir by applying a force to the upper surface of said valve means;

means connected to said port for conveying liquid into said casing to apply a force to said upper surface sufficient to open said valve means and thereby fill said reservoir;

a structure slidably received in said casing; and

the weight of said structure being sufficient to open said valve means when resting thereon.

6. A pumping system as set forth in claim 5 including:

a removable cover closing the upper end of said casing; and

said structure being removable from said casing when said cover is removed from said upper end.

7. A pumping system as set forth in claim 5 wherein:

said structure is a pump and motor unit; and

said casing embodies an enlarged area defining a by pass chamber located above the bottom ofsaid casing a sufficient distance whereby when said pump and motor unit is disposed within said enlarged area, said unit is lifted off said valve means to allow said valve means to close.

8. A pumping system as set forth in claim 5 including:

flat bottom structure means mounted on the bottom of said casing below said valve means; and

valve guide means between said valve means and said flat bottom structure means.

9. A pumping system as set forth in claim 8 wherein:

one of said means includes a cylindrical rod extend ing toward the other of said means;

the other of said means includes a hollow cylindrical member extending toward said one means and slidably receiving said rod to provide said guide means; and

said rod and cylindrical member are coaxial with said casing 10. A pumping system as set forth in claim 9 wherein:

said flat bottom structure means includes a central hub, a rim surrounding said hub and a plurality of spoke elements connecting said rim to said hub, said hub being coaxial with said casing; and

a plurality of upwardly extending support webs formed on said rim, said webs being attached to the bottom of said casing.

ll. A valve assembly for a fluid transmitting casing of a pumping system especially suited for a cryogenic fluid storage reservoir comprising:

a cylindrical upright housing adapted to be fixed to the bottom of said casing;

a foot valve element including a central portion extending upwardly into said housing and a radially extending foot plate underlying the lower end of said housing, an annular valve rim on the upper surface of said foot plate coaxial with said lower end of said housing;

spring means biasing said annular valve rim into sealing engagement with said lower end of said housing;

a flat bottom element below said foot valve element and fixedly attached to said housing; and

valve guide means between 'said foot valve element and said flat bottom element.

12. A valve assembly as set forth in claim 11 wherein said valve guide means comprises:

a hollow cylindrical member on one of said elements slidably receiving a cylindrical rod on the other of said elements, said cylindrical member and said rod being coaxial with said cylindrical housing.

13. A valve assembly as set forth in claim 11 including:

9 10 an outwardly extending annular flange formed on the a plurality of circularly arranged upwardly extending lower end of said housing; support webs on said flat bottom element fixed to an annular seal on the bottom of said flange coaxial said flange outside of said annular seal.

with said valve rim; and 

1. A method of filling a reservoir with a liquid and withdrawing the liquid from the reservoir comprising the steps of: providing a casing in said reservoir extending from the top to a bottom portion of the reservoir, a port at the upper end of said casing, a spring biased normally closed valve means depending from the bottom of said casing, a pump and motor unit slidably received in said casing and resting on said valve means, the weight of said pump and motor unit on said valve means opening the same to communicate the bottom of said casing to said reservoir; lifting said pump and motor unit off of said valve means to close said valve means; conveying said liquid into said casing through said port under sufficient pressure or sufficient liquid head to open said valve means and for sufficient time to fill said reservoir to a predetermined level; thereafter lowering said pump and motor unit onto said valve means to open the same; and energizing said pump and motor unit to withdraw liquid from said reservoir through said casing.
 2. A method as set forth in claim 1 including the step of: withdrawing said pump and motor unit from said casing prior to conveying said liquid into said casing.
 3. A method as set forth in claim 1 including the steps of: providing a by-pass chamber in said casing; and lifting said pump and motor unit into said chamber prior to conveying said liquid into said casing.
 4. A method of filling a reservoir with a liquid and withdrawing the liquid from the reservoir comprising the steps of: providing a casing in said reservoir extending from the top to a bottom portion of the reservoir, a port in the wall of said casing near the upper end thereof, a spring biased normally closed valve means depending from the bottom of said casing adapted to be opened to communicate the bottom of said casing to said reservoir by applying a force to the upper surface of said valve means, and a removable cover closing the upper end of said casing; conveying said liquid into said casing through said port under pressure or at sufficient differential liquid head to apply a force to said upper surface sufficient to open said valve means and for sufficient time to fill said reservoir to a predetermined level; removing said cover from said casing; sliding a pump and motor unit into said casing through said upper end thereof, lowering said unit onto said valve means to open the same; and energizing said pump and motor unit to withdraw liquid from said reservoir through said casing.
 5. A pumping system for a liquid storage reservoir of a ship or the like comprising: a single casing in said reservoir extending from a top to a bottom portion of said reservoir; a port in said casing near the upper end thereof; a spring biased normally closed valve means depending from the bottom of said casing adapted to be opened to communicate the bottom of said casing to said reservoir by applying a force to the upper surface of said valve means; means connected to said port for conveying liquid into said casing to apply a force to said upper surface sufficient to open said valve means and thereby fill said reservoir; a structure slidably received in said casing; and the weight of said structure being sufficient to open said valve means when resting thereon.
 6. A pumping system as set forth in claim 5 including: a removable cover closing the upper end of said casing; and said structure being removable from said casing when said cover is removed from said upper end.
 7. A pumping system as set forth in claim 5 wherein: said structure is a pump and motor unit; and said casing embodies an enlarged area defining a bypass chamber located above the bottom of said casing a sufficient distance whereby when said pump and motor unit is disposed within said enlarged area, said unit is lifted off said valve means to allow said valve means to close.
 8. A pumping system as set forth in claim 5 including: flat bottom structure means mounted on the bottom of said casing below said valve means; and valve guide means between said valve means and said flat bottom structure means.
 9. A pumping system as set forth in claim 8 wherein: one of said means includes a cylindrical rod extending toward the other of said means; the other of said means includes a hollow cylindrical member extending toward said one means and slidably receiving said rod to provide said guide means; and said rod and cylindrical member are coaxial with said casing.
 10. A pumping system as set forth in claim 9 wherein: said flat bottom structure means includes a central hub, a rim surrounding said hub and a plurality of spoke elements connecting said rim to said hub, said hub being coaxial with said casing; and a plurality of upwardly extending support webs formed on said rim, said webs being attached to the bottom of said casing.
 11. A valve assembly for a fluid transmitting casing of a pumping system especially suited for a cryogenic fluid storage reservoir comprising: a cylindrical upright housing adapted to be fixed to the bottom of said casing; a foot valve element including a central portion extending upwardly into said housing and a radially extending foot plate underlying the lower end of said housing, an annular valve rim on the upper surface of said foot plate coaxial with said lower end of said housing; spring means biasing said annular valve rim into sealing engagement with said lower end of said housing; a flat bottom element below said foot valve element and fixedly attached to said housing; and valve guide means between said foot valve element and said flat bottom element.
 12. A valve assembly as set forth in claim 11 wherein said valve guide means comprises: a hollow cylindrical member on one of said elements slidably receiving a cylindrical rod on the other of said elements, said cylindrical member and said rod being coaxial with said cylindrical housing.
 13. A valve assembly as set forth in claim 11 including: an outwardly extending annular flange formed on the lower end of said housing; an annular seal on the bottom of said flange coaxial with said valve rim; and a plurality of circularly arranged upwardly extending support webs on said flat bottom element fixed to said flange outside of said annular seal. 